/**
 * 724. 寻找数组的中心下标
 * https://leetcode.cn/problems/find-pivot-index/description/
 */
class Solution3 {
    public int pivotIndex(int[] nums) {
        int n = nums.length;
        int[] f = new int[n], g = new int[n];

        f[0] = 0; g[n - 1] = 0;

        for(int i = 1; i < n; i++) {
            f[i] = f[i - 1] + nums[i - 1];
        }

        for(int i = n - 2; i >= 0; i--) {
            g[i] = g[i + 1] + nums[i + 1];
        }

        for(int i = 0; i < n; i++) {
            if(f[i] == g[i]) return i;
        }

        return -1;
    }
}